The invention relates to administering apparatus and methods, including injection apparatus. Such administering apparatus include those provided for medical, therapeutic, diagnostic, pharmaceutical or cosmetic applications, among other uses. More particularly, the present invention relates to administering apparatus, such as injection apparatus and devices, which allow a dose to be selected. Examples include injection pens, in particular semi-disposable pens, however, an administering apparatus in accordance with the present invention may also take the form of an inhalation apparatus or an apparatus for dispensing a product to be ingested orally, in doses.
Administering apparatus should generally be easy to handle and therefore small, yet should exhibit as high a degree of functionality, accuracy, ease of use as possible. So-called injection pens, which are referred to as such due to their slim shape, automatically fulfill the first aspect. One aspect with regard to functionality is the capacity to freely select the product dosage to be injected in an injection. The option of selecting the product dose is advantageous, including in those applications in which a user administers the product to be injected him/herself, as is common in diabetes therapy or administering hormones, to name but two exemplary applications. In known devices, the option of flexibly selecting the product dosage, however, involves a corresponding technical complexity which not only increases the price, but also enlarges the apparatus in question.
An injection pen in which the product dosage may be selected is described in U.S. Pat. No. 4,973,318. The pen comprises a piston rod which is formed by a threaded rod and serves to shift a piston in a product ampoule and so deliver the product. The pen comprises a front casing sleeve and a rear casing sleeve which can be rotated relative to each other about a common longitudinal axis. The product dosage is selected by relatively rotating the two casing sleeves. The piston rod is in threaded engagement with a threaded nut. The threaded nut forms a front section of a sleeve-shaped dosing and activating element. This dosing and activating element protrudes into the rear casing sleeve at a rear end and is connected, secured against rotating, to the rear casing sleeve, but can be shifted back and forth relative to the rear casing sleeve in the longitudinal direction of the piston rod. If the rear casing sleeve is rotated for the purpose of selecting the dosage, then the dosing and activating element compulsorily rotates with it. Since, however, the piston rod is connected, secured against rotating, to the front casing sleeve, the rotational movement moves the dosing and activating element further backwards, out of the rear casing sleeve. This increases the overall length of the arrangement of the piston rod and the dosing and activating element, and increases a slight distance between the front end of the dosing and activating element and a stopper area of the casing. This slight distance corresponds to the maximum possible stroke when the dosing and activating element is advanced, together with the piston rod, towards a front end of the pen, for the purpose of delivering the product. Due to this very simple dosing mechanism, the stroke of the delivery movement corresponds to the respectively set product dosage and is thus variable.
An injection pen is known from WO 97/17096 which always exhibits the same delivery stroke, irrespective of the selected product dosage. The piston rod is likewise formed as a threaded rod and connected, secured against rotating, to the casing of the pen. A dosage setting nut is in threaded engagement with the piston rod. The piston rod protrudes into a sleeve-shaped dosing and activating element. The dosing and activating element and the dosage setting nut of this pen are separate parts. The dosing and activating element is connected, secured against rotating, to the dosage setting nut, but can be shifted in the longitudinal direction of the piston rod. For this engagement, the dosing and activating element surrounds the dosage setting nut. For selecting the product dosage, the dosing and activating element is rotated about the longitudinal axis, wherein the dosage setting nut is rotated with it. Since the dosage setting nut is in threaded engagement with the piston rod, linearly guided on the casing, and since the piston rod is blocked against moving counter to the advancing direction, the dosage setting nut is moved backwards and therefore deeper into the dosing and activating element, during its rotational movement along the piston rod. A slight distance results between the front end of the dosage setting nut and a stopper of the casing lying opposite in the advancing direction, said slight distance corresponding to the path which the piston rod and the dosage setting nut can jointly travel during the delivery movement, and thus to the product dosage. To form the connection, secured against rotating, between the dosing and activating element and the dosage setting nut, it is necessary for these two parts to overlap along the longitudinal axis, which increases the diameter of the pen. When using the dosing mechanism in a semi-disposable injection pen, assembling the parts of such a pen is made more difficult if the dosage setting nut and the dosing and activating element are each components of parts of the pen which have to be connected to each other.